Resilient well cement compositions and methods

ABSTRACT

The present invention provides resilient cement compositions and methods which are particularly useful in the construction and repair of oil and gas wells. The cement compositions have improved mechanical properties including elasticity and ductility.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No. 08/839,839 filed on Apr. 17, 1997 which is a continuation of application Ser. No. 08/673,987 filed on Jul. 1, 1996, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to cementing subterranean wells, and more particularly, to cement compositions and methods whereby the compositions set into highly resilient solid masses.

2. Description of the Prior Art

Hydraulic cement compositions are commonly utilized in subterranean well completion and remedial operations. For example, hydraulic cement compositions are used in primary cementing operations whereby pipes such as casings and liners are cemented in well bores. In performing primary cementing, a hydraulic cement composition is pumped into the annular space between the walls of the well bore and the exterior surfaces of pipe disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened substantially impermeable cement therein. The cement sheath physically supports and positions the pipe in the well bore and bonds the exterior surfaces of the pipe to the walls of the well bore whereby the undesirable migration of fluids between zones or formations penetrated by the well bore is prevented. The cement compositions utilized in primary cementing must often be lightweight to prevent excessive hydrostatic pressures from being exerted on formations penetrated by well bores.

The transition time of a well cement composition is the time after its placement in a subterranean zone penetrated by a well bore during which the cement composition changes from a true fluid to a hard set mass. During the transition time, the cement composition becomes partially self-supporting which lowers the hydrostatic pressure exerted by the cement composition on formations containing pressurized fluid penetrated by the well bore. That is, when the cement composition becomes partially self-supporting, volume reductions in the cement composition caused by fluid loss to adjacent formations and hydration of the cement result in rapid decreases in the hydrostatic pressure exerted by the cement composition. When the fluid phase within the cement matrix is not compressible and the pressure exerted by the cement composition falls below the pressure of formation fluids, the formation fluids enter the annulus and flow through the cement composition forming undesirable flow passages which remain after the cement composition sets. The use of a highly compressible fluid component, like gas, in the cement composition improves the composition's ability to maintain pressure and thus prevents the flow of formation fluids into and/or through the cement composition.

The development of wells including one or more laterals to increase production has recently taken place. Such multi-lateral wells include vertical or deviated (including horizontal) principal well bores having one or more ancillary laterally extending well bores connected thereto. Drilling and completion equipment has been developed which allows multiple laterals to be drilled from a principal cased and cemented well bore. Each of the lateral well bores can include a liner cemented therein which is tied into the principal well bore. The lateral well bores can be vertical or deviated and can be drilled into predetermined producing formations or zones at any time in the productive life cycle of the well.

In both conventional single bore wells and multi-lateral wells having several bores, the cement composition utilized for cementing casing or liners in the well bores must develop high bond strength after setting and also have sufficient resiliency, i.e., elasticity and ductility, to resist loss of pipe or formation bond, cracking and/or shattering as a result of pipe movement, impacts and/or shocks subsequently generated by drilling and other well operations. The bond loss, cracking and/or shattering of the set cement allows leakage of formation fluids through at least portions of the well bore or bores which can be highly detrimental.

Set cement in wells, and particularly the set cement forming the cement sheaths in the annuli between pipes and the walls of well bores, often fail due to shear and compressional stresses exerted on the set cement. Such stress conditions are commonly the result of relatively high fluid pressures and/or temperatures inside pipe cemented in well bores during testing, perforating, fluid injection and/or fluid production. The high internal pipe pressure and/or temperature results in expansion of the pipe, both radially and longitudinally, which places stresses on the cement sheath causing it to crack or the bonds between the exterior surfaces of the pipe and/or the well bore walls and the cement sheath to fail in the form of loss of hydraulic seal.

Another condition results from exceedingly high pressures which occur inside the cement sheath due to the thermal expansion of fluids trapped within the cement sheath. This condition often occurs as a result of high temperature differentials created during the injection or production of high temperature fluids through the well bore, e.g., wells subjected to steam recovery or the production of hot formation fluids from high temperature formations. Typically, the pressure of the trapped fluids exceeds the collapse pressure of the cement and pipe causing leaks and bond failure. Yet another compressional stress condition occurs as a result of outside forces exerted on the cement sheath due to formation shifting and overburden pressures.

In multi-lateral wells wherein pipe has been cemented in well bores using conventional well cement slurries which set into brittle solid masses, the brittle set cement cannot withstand impacts and shocks subsequently generated by drilling and other well operations carried out in the multiple laterals without cracking or shattering.

The above described failures can result in loss of production, environmental pollution, hazardous rig operations and/or hazardous production operations. The most common hazard is the presence of gas pressure at the well head.

Thus, there are needs for well cement compositions and methods whereby after setting the cement compositions are highly resilient and can withstand the above described stresses without failure. That is, there is a need for well cement compositions and methods whereby the set cement has improved mechanical properties including elasticity and ductility and failures due to pipe movement, impacts and shocks are reduced or prevented.

SUMMARY OF THE INVENTION

The present invention provides highly resilient well cement compositions having improved mechanical properties including elasticity and ductility and methods of using the compositions which meet the needs described above and overcome the deficiencies of the prior art. A well cement composition of this invention is comprised of a hydraulic cement, fumed silica present in an amount in the range of from about 5% to about 30% by weight of hydraulic cement in the composition, an aqueous rubber latex present in an amount in the range of from about 2.5% to about 45% by weight of hydraulic cement in the composition and an effective amount of a latex stabilizer.

Another well cement composition of this invention is comprised of a hydraulic cement, fumed silica present in an amount in the range of from about 5% to about 30% by weight of hydraulic cement in the composition, an aqueous rubber latex present in an amount in the range of from about 2.5% to about 45% by weight of hydraulic cement in the composition, and effective amounts of a latex stabilizer, a defoaming agent, a gas, a foaming agent and a foam stabilizer. In addition to being highly resilient, this foamed cement composition is lightweight and contains a compressible gas whereby pressurized formation fluid migration through the setting cement is prevented.

Another foamed cement composition of this invention is comprised of a hydraulic cement, fumed silica present in an amount in the range of from about 5% to about 30% by weight of hydraulic cement in the composition, water present in an amount in the range of from about 22% to about 95% by weight of hydraulic cement in the composition, and effective amounts of a gas, a foaming agent and a foam stabilizer.

Yet another foamed cement composition of this invention is comprised of a hydraulic cement, an aqueous rubber latex present in an amount in the range of from about 2.5% to about 45% by weight of hydraulic cement in the composition, and effective amounts of a latex stabilizer, a defoaming agent, a gas, a foaming agent and a foam stabilizer.

The methods of the invention basically comprise the steps of introducing a well cement composition of this invention which sets into a high bond strength, highly resilient solid mass having elasticity and ductility into a subterranean well and allowing the cement composition to set in the well.

It is, therefore, a general object of the present invention to provide improved resilient well cement compositions and methods.

Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides resilient well cement compositions having improved mechanical properties including elasticity and ductility and methods of utilizing the resilient cement compositions in cementing operations carried out in subterranean wells. While the compositions and methods are useful in a variety of well completion and remedial operations, they are particularly useful in primary cementing, i.e., cementing casings and liners in well bores including the cementing of multi-lateral subterranean wells.

A non-foamed well cement composition of this invention is basically comprised of a hydraulic cement, fumed silica present in an amount in the range of from about 5% to about 30% by weight of hydraulic cement in the composition (from about 4.5 pounds to about 30 pounds per 94 pound sack of cement), an aqueous rubber latex present in an amount in the range of from about 2.5% to about 45% by weight of hydraulic cement in the composition (from about 0.25 gallons to about 5 gallons per 94 pound sack of cement) and an effective amount of a latex stabilizer.

A variety of hydraulic cements can be utilized in accordance with the present invention including those comprised of calcium, aluminum, silicon, oxygen and/or sulfur which set and harden by reaction with water. Such hydraulic cements include Portland cements, pozzolana cements, gypsum cements, high aluminum content cements, silica cements and high alkalinity cements. Portland cements are generally preferred for use in accordance with the present invention. Portland cements of the types defined and described in API Specification For Materials And Testing For Well Cements, API Specification 10, 5th Edition, dated Jul. 1, 1990 of the American Petroleum Institute are particularly suitable. Preferred API Portland cements include classes A, B, C, G and H, with API classes G and H being more preferred and class G being the most preferred.

Fumed silica is a colloidal form of silica made by the combustion of silicon tetrachloride in hydrogen-oxygen furnaces. Fumed silica is of a fine particle size, and in combination with the other components of the cement compositions of this invention provides improved mechanical properties to the compositions, particularly the ability to withstand a wide range of stresses associated with subterranean well conditions without bond loss, cracking, shattering or other form of failure. The term "fumed silica" is used herein to mean the fumed silica made as described above and equivalent forms of silica made in other ways.

The fumed silica is present in the above described composition of this invention in an amount in the range of from about 5% to about 30% by weight of the hydraulic cement in the composition (from about 4.5 to about 30 lb/sack), more preferably from about 7.5% to about 15% (from about 7 to about 14 lb/sack) and most preferably about 10% (about 9.4 lb/sack). As will be understood by those skilled in the art, the fumed silica reacts with lime and the like liberated by the hydraulic cement during hydration to form an amorphous metal silicate hydrate.

A variety of well known rubber materials can be utilized in accordance with the present invention. Such materials are commercially available in aqueous latex form, i.e., aqueous dispersions or emulsions. For example, natural rubber (cis-1,4-polyisoprene) and most of its modified types can be utilized. Synthetic polymers of various types can also be used including styrene/butadiene rubber, cis-1,4-polybutadiene rubber and blends thereof with natural rubber or styrene/butadiene rubber, high styrene resin, butyl rubber, ethylene/propylene rubbers, neoprene rubber, nitrile rubber, cis-1,4-polyisoprene rubber, silicone rubber, chlorosulfonated rubber, polyethylene rubber, epichlorohydrin rubber, fluorocarbon rubber, fluorosilicone rubber, polyurethane rubber, polyacrylic rubber and polysulfide rubber.

Of the various latexes which can be utilized, those prepared by emulsion polymerization processes are preferred. A particularly preferred latex for use in accordance with this invention is a styrene/butadiene copolymer latex emulsion prepared by emulsion polymerization. The aqueous phase of the emulsion is an aqueous colloidal dispersion of the styrene/butadiene copolymer. The latex dispersion usually includes water in an amount in the range of from about 40% to about 70% by weight of the latex, and in addition to the dispersed styrene/butadiene particles, the latex often includes small quantities of an emulsifier, polymerization catalysts, chain modifying agents and the like. The weight ratio of styrene to butadiene in the latex can range from about 10%:90% to about 90%:10%.

It is understood that styrene/butadiene latexes are often commercially produced as terpolymer latexes which include up to about 3% by weight of a third monomer to assist in stabilizing the latex emulsions. The third monomer, when present, generally is anionic in character and includes a carboxylate, sulfate or sulfonate group. Other groups that may be present on the third monomer include phosphates, phosphonates or phenolics. Non-ionic groups which exhibit stearic effects and which contain long ethoxylate or hydrocarbon tails can also be present.

A particularly suitable styrene/butadiene aqueous latex has a styrene/butadiene weight ratio of about 25%:75%, and the styrene/butadiene copolymer is suspended in a 50% by weight aqueous emulsion. This styrene/butadiene aqueous latex in combination with the other components of the cement compositions of this invention provides excellent resiliency to a set cement composition without the appreciable loss of bond strength in the set cement. A latex of this type is available from Halliburton Energy Services of Duncan, Oklahoma under the trade designation "LATEX 2000™." The aqueous latex used is included in the cement compositions of this invention in an amount in the range of from about 2.5% to about 45% by weight of the hydraulic cement in the composition (from about 0.25 to about 5.0 gal/sack), more preferably from about 4.5% to about 22% (from about 0.5 to about 2.5 gal/sack) and most preferably about 9% (about 1 gal/sack).

In order to prevent the aqueous latex from prematurely coagulating and increasing the viscosity of the cement composition, an effective amount of a latex stabilizer is included in the cement composition. Latex stabilizers are comprised of one or more surfactants which function to prevent latex coagulation. Those which are particularly suitable for use in accordance with the present invention are surfactants having the formula

    R--Ph--O(O CH.sub.2 CH.sub.2 ).sub.m OH

wherein R is an alkyl group having from about 5 to about 30 carbon atoms, Ph is phenyl and m is an integer in the range of from about 5 to about 50, and surfactants of the general formula

    R.sub.1 (OR.sub.2).sub.n SO.sub.3 X

wherein R₁ is selected from the group consisting of alkyl groups having from 1 to about 30 carbon atoms, cycloalkyl groups having 5 or 6 carbon atoms, C₁ -C₄ alkyl substituted cycloalkyl groups, phenyl, alkyl substituted phenyl of the general formula (R₃)_(a) Ph- wherein Ph is phenyl, R₃ is an alkyl group having from 1 to about 18 carbon atoms and a is an integer of from 1 to 3, and phenyl-alkyl groups wherein the alkyl groups have from 1 to about 18 carbon atoms and the phenyl-alkyl groups have a total of from about 8 to about 28 carbon atoms, R₂ is a substituted ethylene group of the formula --CH₂ CH₂ R₄ wherein R₄ is selected from hydrogen, methyl, ethyl or mixtures thereof, and n is a number from 0 to about 40 provided that when R₁ is phenyl or alkyl substituted phenyl n is at least one, and X is any compatible cation. A preferred surfactant in this group is ethoxylated nonylphenyl containing in the range of from about 20 to about 30 moles of ethylene oxide.

Another preferred surfactant in the group is a sodium salt having the general formula

    R.sub.5 --Ph(OR.sub.6).sub.o SO.sub.3 X

wherein R₅ is an alkyl group having in the range of from 1 to about 9 carbon atoms, R₆ is the group --CH₂ CH₂ --, o is an integer from about 10 to about 20 and X is a compatible cation.

Yet another preferred surfactant in the group is a sodium salt having the formula

    R.sub.7 (OR.sub.8).sub.p SO.sub.3 X

wherein R₇ is an alkyl group having in the range of from about 5 to about 20 carbon atoms, R₈ is the group --CH₂ CH₂ --, p is an integer in the range of from about 10 to about 40 and X is a compatible cation. A particularly preferred surfactant of this type is the sodium salt of a sulfonated compound derived by reacting a C₁₂ to C₁₅ alcohol with about 15 moles of ethylene oxide having the formula

    H(CH.sub.2).sub.12-15 (CH.sub.2 CH.sub.2 O).sub.15 SO.sub.3 Na

which is commercially available under the name "AVANEL S150™" from PPG Mazer, Mazer Chemicals, a Division of PPG Industries, Inc., 3938 Porett Drive, Gurnee, Ill. 60031.

Of the various latex stabilizers described above which can be used, ethoxylated nonylphenol containing in the range of from about 15 to about 40 moles of ethylene oxide and the "AVANEL™" series of surfactants, i.e., the sodium salt of a sulfonated and ethoxylated compound having the formula H(CH₂)₁₂₋₁₅ (CH₂ CH₂ O)₁₅₋₄₀ SO₃ Na are preferred, with H(CH₂)₁₂₋₁₅ (CH₂ CH₂ O)₁₅ SO₃ Na being the most preferred.

While different amounts of latex stabilizer are included in the cement composition depending on the particular aqueous rubber latex used, the latex stabilizer is usually included in the cement composition in an amount in the range of from about 9% to about 35% by weight of the aqueous rubber latex included therein (from about 0.02 to about 1.75 gal/sack of cement). When the aqueous latex is an aqueous styrene/butadiene latex, the latex stabilizer utilized is preferably included in the cement composition in an amount in the range of from about 9% to about 35% by weight of the aqueous rubber latex included in the composition (from about 0.02 to about 1.75 gal/sack of cement), more preferably from about 15% to about 25% (from about 0.04 to about 1.25 gal/sack) and most preferably about 20% (about 0.2 gal/sack).

While the water in the aqueous rubber latex used in forming the cement compositions of this invention which contain an aqueous rubber latex can be adequate for producing a pumpable slurry and hydrating the cementitious materials therein, additional water can be added to the compositions as required for pumpability. Also, water must be added to the compositions that do not include an aqueous rubber latex in an amount at least sufficient to form a pumpable slurry.

The water can be from any source provided it does not contain in excess of compounds that adversely affect other components in the cement compositions. For example, the water can contain various salts such as sodium, potassium and calcium chloride or the like. Generally, water is present in a cement slurry composition of this invention in an amount in the range of from about 22% to about 95% by weight of hydraulic cement therein (from about 2.5 to about 10.7 gal/sack).

A light weight, foamed, highly resilient well cement composition of this invention is comprised of a hydraulic cement of the type described above, fumed silica as described above present in an amount in the range of from about 5% to about 30% by weight of hydraulic cement in the composition (from about 4.5 to about 30 lb/sack), an aqueous rubber latex of the type described above present in an amount in the range of from about 2.5% to about 45% by weight of hydraulic cement in the composition (from about 0.25 to about 5.0 gal/sack), an effective amount of a latex stabilizer of the type described above, an effective amount of a defoaming agent, a compressible gas present in an amount sufficient to foam the composition and produce a density in the range of from about 8 pounds per gallon to about 16 pounds per gallon, an effective amount of a foaming agent and an effective amount of a foam stabilizer.

The defoaming agent prevents foaming during mixing of the cement composition prior to foaming the composition. That is, because the aqueous rubber latex includes surfactants for emulsifying the latex and latex stabilizer which also function as foaming agents, a large bubble, unstable foam is produced when the hydraulic cement and silica are mixed with the latex. The defoaming agent prevents the formation of the large bubble foam so that a small bubble stable foam can be subsequently formed. The defoaming agent can comprise any of the compounds well known for such capabilities such as the polyol silicon compounds. A preferred such defoaming agent is polydimethylsiloxane which is commercially available from Halliburton Energy Services of Duncan, Okla., under the trade designation "D-AIR™." The defoaming agent is generally included in the cement composition in an amount in the range of from about 0.1% to about 0.9% by weight of the hydraulic cement therein (from about 0.01 to about 0.1 gal/sack), more preferably from about 0.18% to about 0.7% (from about 0.02 to about 0.08 gal/sack) and most preferably about 0.18% (about 0.02 gal/sack).

The compressible gas functions to foam the cement composition, to prevent pressurized formation fluid influx into the cement composition when setting and contributes to the resiliency of the set composition. The gas is preferably nitrogen or air, with nitrogen being the most preferred. Generally, the gas is present in an amount sufficient to foam the cement slurry and produce a slurry density in the range of from about 8 to about 16 pounds per gallon, more preferably from about 12 to about 15 pounds per gallon and most preferably about 13 pounds per gallon. The amount of gas which is present in a foamed cement composition of this invention generally ranges from about 8.5% to about 50% by volume of the resulting foamed cement composition.

In order to facilitate foaming and to stabilize the foamed slurry, a foaming agent is included in the cement composition. Suitable foaming agents are surfactants having the general formula:

    H(CH.sub.2).sub.a (OC.sub.2 H.sub.4 ).sub.b OSO.sub.3 X

wherein:

a is an integer in the range of from about 5 to about 15;

b is an integer in the range of from about 1 to about 10; and

X is any compatible cation.

A particularly preferred foaming agent is a surfactant of the above type having the formula:

    H(CH.sub.2).sub.a (OC.sub.2 H.sub.4).sub.3 OSO.sub.3 Na

wherein:

a is an integer in the range of from about 6 to about 10. This surfactant is commercially available from Halliburton Energy Services of Duncan, Okla., under the trade designation "CFA-S™."

Another particularly preferred foaming agent of the above mentioned type is a surfactant having the formula:

    H(CH.sub.2).sub.a (OC.sub.2 H.sub.4).sub.b OSO.sub.3 NH.sub.4

wherein:

a is an integer in the range of from about 5 to about 15; and

b is an integer in the range of from about 1 to about 10.

This surfactant is available from Halliburton Energy Services under the trade name "HALLIBURTON FOAM ADDITIVE™."

Another foaming agent which can be utilized in the cement compositions of this invention includes polyethoxylated alcohols having the formula:

    H(CH.sub.2).sub.a (OC.sub.2 H.sub.4).sub.b OH

wherein:

a is an integer in the range of from about 10 to about 18; and

b is an integer in the range of from about 6 to about 15.

This surfactant is available from Halliburton Energy Services under the trade name "AQF-1™."

Yet another foaming agent which can be used is a sodium salt of alpha-olefinic sulfonic acid (AOS) which is a mixture of compounds of the formulas:

    X H(CH.sub.2).sub.n --C=C--(CH.sub.2).sub.m SO.sub.3 Na!

and

    Y H(CH.sub.2).sub.p --COH--(CH.sub.2).sub.q SO.sub.3 Na!

wherein:

n and m are individually integers in the range of from about 6 to about 16;

p and q are individually integers in the range of from about 7 to about 17; and

X and Y are fractions with the sum of X and Y being 1. This foaming agent is available from Halliburton Energy Services under the trade name "AQF-2™."

Still another foaming surfactant which can be used is an alcohol ether sulfate of the formula:

    H(CH.sub.2).sub.a (OC.sub.2 H.sub.4).sub.b SO.sub.3 NH.sub.4

wherein:

a is an integer in the range of from about 6 to about 10; and

b is an integer in the range of from about 3 to about 10.

The particular foaming agent employed will depend on various factors such as the types of formations in which the foamed cement is to be placed. Generally, the foaming agent utilized is included in a cement composition of this invention in an amount in the range of from about 1.5% to about 10% by weight of water in the composition. When the foaming agent is one of the preferred surfactants described above, it is included in the composition in an amount in the range of from about 4% to about 9.5% by weight of water therein.

A foam stabilizer is also included in the foamed cement composition to enhance the stability of the foamed cement slurry. One such foam stabilizing agent is a compound of the formula: ##STR1## wherein: R is hydrogen or a methyl radical; and

n is an integer in the range of from about 20 to about 200.

A particularly preferred foam stabilizing agent of the above type is a methoxypolyethylene glycol of the formula:

    CH.sub.3 O(CH.sub.2 CH.sub.2 O).sub.n CH.sub.2 OH

wherein:

n is in the range of from about 100 to about 150. This foam stabilizing agent is commercially available from Halliburton Energy Services under the trade designation "HALLIBURTON FOAM STABILIZER™."

The preferred foam stabilizing agent is a compound having the formula:

    R--CONHCH.sub.2 CH.sub.2 CH.sub.2 N.sup.+ (CH.sub.3).sub.2 CH.sub.2 CO.sub.2 .sup.-

wherein:

R is a C₁₀ to C₁₈ saturated aliphatic hydrocarbon group or an oleyl group or a linoleyl group.

A particularly preferred stabilizing agent of the above type is an amidopropylbetaine of the formula:

    R--CONHCH.sub.2 CH.sub.2 CH.sub.2 N.sup.+ (CH.sub.3).sub.2 CH.sub.2 CO.sub.2 .sup.-

wherein:

R is a cocoyl group. This foam stabilizing agent is commercially available from Halliburton Energy Services under the trade designation "HC-2™."The foam stabilizer is included in a cement composition of this invention in an amount in the range of from about 0.75% to about 5% by weight of water utilized. When the foam stabilizing agent is one of the particularly preferred agents described above, it is preferably present in the composition in an amount in the range of from about 2% to about 5% by weight of water.

Another lightweight, foamed, highly resilient well cement composition of this invention is comprised of a hydraulic cement of the type described above, fumed silica as described above present in an amount in the range of from about 5% to about 30% by weight of hydraulic cement in the composition (from about 4.5 to about 30 lb/sack), water present in an amount in the range of from about 22% to about 95% by weight of hydraulic cement in the composition (from about 2.5 gal/sack to about 10.7 gal/sack), a compressible gas present in an amount sufficient to foam the composition and produce a density in the range of from about 8 pounds per gallon to about 16 pounds per gallon, an effective amount of a foaming agent and an effective amount of a foam stabilizer.

This foamed cement composition does not include an aqueous rubber latex, but it has unexpected and surprisingly improved physical and mechanical properties including high degrees of elasticity and ductility and a high resistance to pressurized formation fluid migration.

Yet another foamed well cement composition of this invention is comprised of a hydraulic cement of the type described above, an aqueous rubber latex described above present in an amount in the range of from about 2.5% to about 45% by weight of hydraulic cement in the composition (from about 0.25 to about 5 gal/sack), an effective amount of a latex stabilizer described above, an effective amount of a defoaming agent described above, a compressible gas described above present in an amount sufficient to foam the cement composition and produce a cement composition density in the range of from about 8 pounds per gallon to about 16 pounds per gallon, an effective amount of a foaming agent described above and an effective amount of a foam stabilizer described above.

This foamed cement composition which is useful in some applications does not include fumed silica, but it is also light weight, resilient and resists pressurized formation fluid migration.

The well cement compositions useful herein can include other additives which are well known to those skilled in the art including fluid loss control additives, set retarding additives, dispersing agents, formation conditioning additives, set accelerators and the like.

Dispersing agents can be utilized to facilitate the use of lower quantities of water and to promote higher set cement strength. A particularly suitable dispersing agent for use with the well cement compositions of this invention is comprised of the condensation polymer product of an aliphatic ketone, an aliphatic aldehyde and a compound which introduces acid groups into the polymer, e.g., sodium sulfite. Such a dispersant is described in U.S. Pat. No. 4,557,763 issued to George et al. on Dec. 10, 1985 which is incorporated herein by reference.

Examples of fluid loss control additives are cellulose derivatives such as carboxymethylhydroxyethylcellulose, hydroxyethylcellulose, modified polysaccharides, polyacrylamides, guar gum derivatives, 2-acrylamido-2-methylpropane sulfonic acid copolymers, polyethyleneimine and the like.

Set retarding additives are included in the cement compositions when it is necessary to extend the time in which the cement composition can be pumped so that it will not thicken or set prior to being placed at a desired location in the well being cemented. Examples of set retarders which can be used include lignosulfonates such as calcium and sodium lignosulfonate, organic acids such as tartaric acid and gluconic acid, copolymers and others. The proper amount of retarder required for particular conditions can be determined by conducting a "thickening time test" for the particular retarder and cement composition. Such tests are described in the API Specification For Materials and Testing for Well Cements, API Specification 10 mentioned above.

A particularly preferred set retarder for use in accordance with the present invention is a copolymer or copolymer salt of 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid. The copolymer comprises from about 40 to about 60 mole percent 2-acrylamido-2-methylpropanesulfonic acid with the balance comprising acrylic acid, and the copolymer or salt preferably has an average molecular weight below about 5,000. This copolymer set retarder is preferably utilized in the composition when the bottom hole circulating temperature exceeds about 200° F. The retarder has been found to both retard the setting of the cement at elevated formation temperatures and to stabilize the aqueous styrene/butadiene latex against agglomeration or inversion at the elevated temperature. The set retarder is generally added to the cement composition in an amount in the range of from about 0.1% to about 6% by weight of hydraulic cement in the composition.

The cement compositions of this invention may be prepared in accordance with any of the well known mixing techniques so long as the latex and latex stabilizing surfactant are not directly admixed without prior dilution by other liquids present. In one preferred method, a quantity of water is introduced into a cement blender and defoamer, latex and latex stabilizer are then sequentially added with suitable agitation to disperse the constituents. Any other liquid additives may then be admixed with the slurry followed by the hydraulic cement, fumed silica and other dry solids. The mixture is agitated for a sufficient period of time to admix the components and form a pumpable non-foamed slurry. When the slurry is foamed, it is pumped to the well bore and the foaming agent and foam stabilizer followed by the gas are injected into the slurry on the fly. As the slurry and gas flow through the well bore to the location where the resulting foamed cement composition is to be placed, the cement composition is foamed and stabilized.

The methods of this invention for cementing a zone in a well basically comprise the steps of placing a cement composition of this invention which sets into a highly resilient, high bond strength, substantially impermeable mass in the subterranean zone to be cemented, and maintaining the cement composition in the zone for a time sufficient for the cement composition to set therein.

In order to further illustrate the improved cement compositions and methods of this invention, the following examples are given.

EXAMPLE 1

Test samples of non-foamed cement compositions of this invention comprised of API Portland Class H hydraulic cement, fumed silica, a dispersant, an aqueous styrene/butadiene latex, a latex stabilizer, and a defoaming agent were prepared. Two of the test samples also included an expansion additive. Descriptions of the test samples are set forth in Table I below.

Portions of each of the test samples were placed in shear bond and hydraulic bond test apparatus and allowed to set for time periods of 1 week at a temperature of 140° F. and atmospheric pressure. The test samples were then tested for shear bond strength and hydraulic bond strength.

The shear bond strength of set cement in the annulus between a pipe disposed in a well bore and the walls of the well bore is defined as the strength of the bond between the set cement and a pipe mechanically supported by the cement. The test sample shear bond strengths were determined by measuring the force required to initiate movement of pipe sections cemented by the test samples in test apparatus simulating a well bore, i.e., larger diameter pipe sections. The determined forces were divided by the cement-pipe contact surface areas to yield the shear bond strengths in psi.

The hydraulic bond strength of the set cement blocks migration of pressurized fluids in a cemented annulus. The test sample hydraulic bond strengths were determined by applying pressure at the pipe-set cement interfaces until leakage occurred. The hydraulic bond strength of a set cement test sample in psi is equal to the hydraulic pressure applied when leakage took place. The results of these tests are also set forth in Table I below.

                                      TABLE I                                      __________________________________________________________________________     Non-Foamed Cement Composition Bond Strength Test Results                       Cement Composition Components                                                               Fumed                                                                               Aqueous                                                                             Latex Expansion                                                                           Defoaming                                                 Silica,                                                                             Latex.sup.1,                                                                        Stabilizer.sup.2,                                                                    Additive.sup.3,                                                                     Agent.sup.4,                                                                        Water,                                                                              Dispersant.sup.5,                                                                       Shear                                                                              Hydraulic                          % by gal per                                                                             gal per                                                                              % by gal per                                                                             % by % by     Bond                                                                               Bond                  Sample                                                                             Hydraulic                                                                               Weight                                                                              94 lb sack                                                                          94 lb sack                                                                           Weight                                                                              94 lb sack                                                                          Weight                                                                              Weight                                                                              Density,                                                                           Strength,                                                                          Strength,             No. Cement   of Cement                                                                           of Cement                                                                           of Cement                                                                            of Cement                                                                           of Cement                                                                           of Cement                                                                           of Cement                                                                           lblgal                                                                             psi psi                   __________________________________________________________________________     1   Portland Class H                                                                        10   0.5  0.05  --   0.02 52.83                                                                               0.5  15   86 1074                  2   Portland Class H                                                                        10   0.5  0.05  5    0.02 55.97                                                                               0.5  15  355 998                   3   Portland Class H                                                                        10   1.0  0.1   --   0.02 47.98                                                                               0.5  15  200 285                   4   Portland Class H                                                                        10   1.0  0.1   5    0.02 51.12                                                                               0.5  15  292 290                   __________________________________________________________________________      .sup.1 Aqueous styrene/butadiene (25%:75% by wt.) latex containing 50% by      weight water ("LATEX 2000" from Halliburton Energy Services).                  .sup.2 Sodium salt of sulfonated and ethoxylated compound having the           formula H (CH.sub.2).sub.12-15 (CH.sub.2 CH.sub.2 O).sub.15 SO.sub.3 Na        ("AVANEL S150 ™" from PPG Mazer).                                           .sup.3 Cement expansive additive ("MICROBOND M ™" from Halliburton          Energy Services, Duncan, Oklahoma).                                            .sup.4 Polydimethylsiloxane.                                                   .sup.5 Condensation polymer product of ketone, aldehyde and sodium sulfit      ("CFR3 ™" from Halliburton Energy Services of Duncan, Oklahoma).      

From Table I, it can be seen that the non-foamed cement compositions of this invention have excellent shear and hydraulic bond strengths.

EXAMPLE 2

Test samples of foamed cement compositions of this invention comprised of hydraulic cement, fumed silica, an aqueous rubber latex, a latex stabilizer, a defoaming agent, air, a foaming agent and a foam stabilizer were prepared. One of the foamed cement compositions also included hemitite weighting material, 100 mesh sand, a set retarder and a retarder intensifier. For each test sample, an unfoamed cement slurry including the defoaming agent was first prepared utilizing a mixing device. A predetermined amount of the resulting slurry was then placed in a fixed volume blender jar having a stacked blade assembly. The foaming agent and foam stabilizer were then added to the jar and the contents were mixed at high speed. The high speed mixing by the stacked blade assembly caused the slurry to be foamed with air. Descriptions of the test samples are set forth in Table IIA below.

The foamed test samples were allowed to set for 1 week at 140° F. and atmospheric pressure after which portions of the test samples were subjected to various tests to determine their properties. More specifically, shear and hydraulic bond strength tests were conducted in accordance with the procedures of Example 1, and unconfined uniaxial and confined triaxial strength tests were conducted and Young's Moduli (also known as moduli of elasticity) and Poisson's as determined as well as bulk compressibilities, shear moduli and tensile strengths, all in accordance with the standardized tests and procedures of the American Society for Testing and Materials (ASTM) set forth, for example, in ASTM Section D 1456. The results of the tests and determinations are set forth in Table IIB below.

                                      TABLE IIA                                    __________________________________________________________________________     Foamed Cement Compositions                                                     __________________________________________________________________________                 Cement Composition Components                                                  Fumed                                                                          Silica,                                                                        % by                  Fluid                                                    Weight                                                                               Aqueous         Loss Sand                                                of    Rubber                                                                              Latex      Control                                                                             (100                                                Cement,                                                                              Latex.sup.1,                                                                        Stabilizer.sup.2,                                                                    Hemitite,                                                                           Agent.sup.3,                                                                        Mesh),                                              or gal                                                                               gal per                                                                             gal per                                                                              % by % by % by                                    Sample      per 94 lb                                                                            94 lb                                                                               94 Lb Weight                                                                              Weight                                                                              Weight                                  Density,                                                                           Hydraulic                                                                              Sack of                                                                              Sack of                                                                             Sack of                                                                              of   of   of                                      No. Cement  Cement                                                                               Cement                                                                              Cement                                                                               Cement                                                                              Cement                                                                              Cement                                  __________________________________________________________________________     1   Portland Class H                                                                       10%   1    0.2   --   --   --                                      2   Portland Class H                                                                       10%   2    0.2   --   --   --                                      3   Portland Class H                                                                       1.63  1     03.sup.10                                                                           200  0.5  40                                                  gal/sk.sup.9                                                       __________________________________________________________________________     Cement Composition Components                                                           Set                                                                       Set  Retarder                                                                             Defoaming                                                                           Foaming                                                                             Foam                                                      Retarder.sup.4,                                                                     Intensifier.sup.5,                                                                   Agent.sup.6,                                                                        Agent.sup.7,                                                                        Stabilizer.sup.8,                                                                    Water,                                              % by % by  gal per                                                                             % by % by  gal per                                                                            Density                                     Sample                                                                             Weight                                                                              Weight                                                                               94 lb                                                                               Weight                                                                              Weight                                                                               94 lb                                                                              of Base                                     Density,                                                                           of   of    Sack of                                                                             of   of    Sack of                                                                            Slurry,                                                                            Foamed                                  No. Cement                                                                              Cement                                                                               Cement                                                                              Water                                                                               Water Cement                                                                             lb/gal                                                                             lb/gal                                  __________________________________________________________________________     1   --   --    0.02 7.5   3.75 5.41                                                                               15  13.6                                    2   --   --    0.02 9.4  4.7   4.32                                                                               15  13.6                                    3   3.3  2.4   0.02 4.5  2.3   5.01                                                                               22  17                                      __________________________________________________________________________      .sup.1 Aqueous styrene/butadiene (25%:75% by wt.) Latex containing 50% by      weight water ("LATEX 2000 ™" from Unical Corp.).                            .sup.2 Sodium salt of a sulfonated and ethoxylated compound having the         formula H(CH.sub.2).sub.12-15 (CH.sub.2 CH.sub.2 O).sub.15 SO.sub.3 Na         ("AVANEL S150 ™" from PPG Mazer).                                           .sup.3 Copolymer of "AMPS®" and N,Ndimethytacrylamide (U.S. Pat. No.       4,555,269).                                                                    .sup.4 Copolymer of "AMPS®" and acrylic acid (U.S. Pat. No.                4,941,536).                                                                    .sup.5 Tartaric acid.                                                          .sup.6 Polydimethylsiloxane.                                                   .sup.7 Sodium salt of alphaolefinic sulfonic acid.                             .sup.8 Cocoylamidopropylbetaine.                                               .sup.9 Aqueous dispersion of 50% fumed silica by weight of water.              .sup.10 Nonylphenol ethoxylated with 15-40 moles of ethylene oxide             substituted for latex stabilizer described in footnote 2.                

                                      TABLE IIB                                    __________________________________________________________________________     Bond Strength And Resiliency Test Results                                      __________________________________________________________________________                                 Confined Triaxial                                                                    Young'                                       Envelope                                                                             Shear Hydraulic                                                                           Unconfined Uniaxial                                                                             Modulus                                      Friction                                                                             Bond  Bond Young's    Compressive                                                                          (EX 10.sup.6)                                Sample                                                                               Strength,                                                                            Strength,                                                                           Modulus                                                                             Poissons                                                                             Strength,                                                                            Confining Pressure, psi                      No.   psi   psi  (EX 10.sup.6)                                                                       Ratio psi   500 1000                                                                              2000                                  __________________________________________________________________________     1     163 (13.8).sup.1                                                                     630  --   --    1388.sup.2                                                                           0.048                                                                              0.312                                                                             0.091                                 2     154 (13.85).sup.1                                                                    720  --   --    1460.sup.2                                                                           0.076                                                                              0.304                                                                             0.026                                 3     --    --   0.35 0.107 2700.sup.2                                                                           0.26                                                                               0.3                                                                               0.282                                 __________________________________________________________________________     Confined Triaxial                                                                              Plastic    Bulk   Shear                                        Envelope                                                                            Poisson's  Failure,   Compressibility                                                                       Modulus                                                                             Tensile                                 Friction                                                                            Ratio      psi        at 1000                                                                               at 1000                                                                             Strength                                                                            Failure                            Sample                                                                              Confining Pressure, psi                                                                   Confining Pressure, psi                                                                   psi, 10.sup.5                                                                         psi, 10.sup.4                                                                       (Briquet),                                                                          Angle                              No.  500 1000                                                                               2000                                                                              500 1000                                                                              2000                                                                               psi    psi  psi  Degrees                            __________________________________________________________________________     1    0.158                                                                              0.1494                                                                             0.079                                                                             2900                                                                               4200                                                                              4000                                                                               0.94   13.57                                                                               194.sup.3                                                                           31.5                               2    0.090                                                                              0.2883                                                                             0.065                                                                             2255                                                                               3200                                                                              3100                                                                                0.418 11.8 250.sup.3                                                                           19.5                               3    0.086                                                                              0.144                                                                              0.109                                                                             3850                                                                               4925                                                                              6950                                                                               6.2    --   --   22                                 __________________________________________________________________________      .sup.1 The number in parentheses is the test sampte density in lb/gal.         .sup.2 The base pressure was 2220 psi.                                         .sup.3 The base pressure was 286 psi.                                    

From the results set forth in Table IIB, it can be seen that the foamed cement compositions tested have excellent bond strengths and resiliencies.

Example 3

Test samples of additional foamed cement compositions of this invention comprised of hydraulic cement, fumed silica, water, air, a foaming agent and a foam stabilizer were prepared. For each test sample, an unfoamed cement slurry was first prepared utilizing a mixing device. A predetermined amount of the resulting slurry was then placed in a fixed volume blender jar having a stacked blade assembly. The foaming agent and foam stabilizer were then added to the jar and the contents were mixed at high speed. The high speed mixing by the stacked blade assembly caused the slurry to be foamed with air. Descriptions of the test samples are set forth in Table IIIA below.

The foamed test samples were allowed to set for 6 days at 140° F. in atmospheric pressure after which portions of the test samples were subjected to the various tests and determinations described in Example 2 above to determine their properties. The results of these tests and determinations are set forth in Table IIIB below.

                                      TABLE IIIA                                   __________________________________________________________________________     Non-Foamed and Foamed Compositions                                             Components                              Cement Composition                                               Foaming                                                                               Foam   Water,                                                                               Density                                                                             Density                                 Fumed Silica,                                                                         Dispersant.sup.1,                                                                     Agent.sup.2,                                                                          Stabilizer.sup.3,                                                                     gal. per                                                                             of Base                                                                             Of Foamed                   Sample                                                                             Hydraulic                                                                              % By Weight                                                                           % By Weight                                                                           % By Weight                                                                           % By Weight                                                                           94 lb. Sack                                                                          Slurry,                                                                             Slurry,                     No. Cement  Of Cement                                                                             of Cement                                                                             Of Water                                                                              of Water                                                                              of Cement                                                                            lb/gal                                                                              lb/gal.                     __________________________________________________________________________     1   Portland Class G                                                                       10     0.25   --     --     6.55  15   --                          2   Portland Class G                                                                       10     0.25   1.5    0.8    6.55  15   13                          3   Portland Class G                                                                       20     0.75   --     --     7.08  15   --                          4   Portland Class G                                                                       20     0.75   1.5    0.8    7.08  15   13                          __________________________________________________________________________      .sup.1 Condensation polymer product of ketone, aldehyde and sodium sulfit      ("CFR3 ™ from Halliburton Energy Services of Duncan, Oklahoma).             .sup.2 Sodium salt of alphaolefinic sulfonic acid.                             .sup.3 Cocoylamidopropylbetaine.                                         

                                      TABLE IIIB                                   __________________________________________________________________________     Bond Strength And Resiliency Test Results                                      __________________________________________________________________________                                  Confined Triaxial                                                                    Young's                                     Shear     Hydraulic                                                                             Unconfined Uniaxial                                                                              Modulus,                                         Bond Bond   Young's     Compressive                                                                          Ex 10.sup.6                                 Sample                                                                              Strength,                                                                           Strength,                                                                             Modulus,                                                                            Poissons                                                                              Strength,                                                                            Confining Pressure                          No.  psi  psi    Ex 10.sup.6                                                                         Ratio  psi   500  1000                                                                               2000                               __________________________________________________________________________     1       68.8                                                                             264    1.37 0.1038 4433  0.6  0.656                                                                              0.309                              2    1050 470     1.189                                                                              0.0915 2770  0.592                                                                               0.616                                                                              0.198                              3     226 545     1.282                                                                              0.1431 3506  --   0.837                                                                              0.796                              4    1400 315    0.76 0.1372 3949  0.497                                                                               0.44                                                                               0.532                              __________________________________________________________________________     Confined Triaxial                                                                              Plastic                      Failure                               Poissons    Failure,   Bulk   Shear Tensile                                                                             Envelope                              Ratio       psi        Compressibility                                                                       Modulus                                                                              Strength                                                                            Friction                          Sample                                                                             Confining Pressure                                                                         Confining Pressure                                                                        @ 1000 psi,                                                                           @ 1000 psi                                                                           (Briquet),                                                                          Angle,                            No. 500 1000                                                                               2000                                                                               500                                                                               1000                                                                               2000                                                                               10.sup.5 psi                                                                          10 psi                                                                               psi  Degrees                           __________________________________________________________________________     1   0.0948                                                                             0.1119                                                                             0.1291                                                                             5984                                                                              7008                                                                               8856                                                                               2.817  2.95  305  26                                2   0.1669                                                                             0.1426                                                                             0.1347                                                                             4979                                                                              5765                                                                               8035                                                                               2.8721 2.6956                                                                               190  22                                3   --  0.2915                                                                             0.1568                                                                             -- 9394                                                                               12465                                                                              6.6906 3.2404                                                                               490  40                                4   0.165                                                                              0.1294                                                                             0.189                                                                              6569                                                                              6881                                                                               9932                                                                               1.9787 1.9479                                                                               207  31                                __________________________________________________________________________

From the results set forth in Table IIIB, it can be seen that the foamed cement compositions comprised of hydraulic cement, fumed silica, water, air, foaming agent and foam stabilizer have unexpected and surprisingly improved ductility and resiliency properties as primarily shown by the Young's modulus test data.

EXAMPLE 4

Comparative tests were conducted between foamed cement compositions of this invention comprised of hydraulic cement, fumed silica, water, air, a foaming agent and a foam stabilizer and various lightweight unfoamed and foamed compositions of the prior art containing hydraulic cement, fumed silica and other components. The foamed compositions of this invention were prepared in the manner described in Example 3 above and are identified in Table IVA below as samples 1, 2, 3 and 4.

The prior art compositions tested are as follows:

A. The two 9.0 pound per gallon unfoamed cement compositions described in Examples I and II of U.S. Pat. No. 5,188,176 issued to Carpenter on Feb. 23, 1993 comprised of water, hydraulic cement, fumed silica and fly ash microspheres. These compositions are described in Table IVA below and identified as samples 1a and 2a.

B. The 9.0 pound per gallon unfoamed cement composition described in Example II of U.S Pat. No. 5,188,176 issued to Carpenter on Feb. 23, 1993 comprised of water, hydraulic cement, fumed silica, dispersant, fly ash microspheres, styrene-butadiene latex, surfactant and defoamer. This composition is described in Table IVA below and identified as sample 3a.

C. The 9.0 pound per gallon foamed cement composition described in Example 2 of U.S. Pat. No. 4,927,462 issued to Sugama on May 22, 1990 comprised of water, hydraulic cement, fumed silica (substituted for silica flour--see col. 2, lines 43-55), treated chopped polypropylene fibers (substituted for carbon fibers--see col. 2, lines 63-66), air, a foaming agent and a foam stabilizer. This composition is described in Table IVA below and identified as sample 4a.

The unfoamed compositions were prepared using a conventional mixing device. The foamed composition was prepared in the manner described in Example 3 above.

The various test samples were allowed to set for 6 days at 140° F. and atmospheric pressure after which portions of the test samples were subjected to a number of the tests and determinations described in Example 2 above to determine their properties, i.e., unconfined compressive strength tests, tensile strength tests and yield strength tests at 1,000 psi confining pressure were conducted and Young's Moduli and Poisson's ratios were determined. The results of the tests and determinations are set forth in Table IVB below.

                                      TABLE IVA                                    __________________________________________________________________________     Foamed Inventive Cement Compositions And Prior Art Cement                      __________________________________________________________________________     Compositions                                                                                                Foaming                                                                               Foam                                       Density,       Fumed Silica,                                                                         Dispersant.sup.1,                                                                     Agent.sup.2                                                                           Stabilizer.sup.3,                          Sample Hydraulic                                                                              % By Weight                                                                           % By Weight                                                                           % By Weight                                                                           % By Weight                                No.    Cement  Of Cement                                                                             Of Cement                                                                             Of Water                                                                              Of Water                                   __________________________________________________________________________     1 (Inventive)                                                                         Portland Class C                                                                       10%    --     2.08   1.12                                       1a (Prior Art)                                                                        Portland Class C                                                                       10%    --     --                                                2 (Inventive)                                                                         Portland Class C                                                                       10%    --     2.08   1.12                                       2a (Prior Art)                                                                        Portland Class C                                                                       10%    --     --     --                                         3 (Inventive)                                                                         Portland Class G                                                                       10%    --     2.08   1.12                                       3a (Prior Art)                                                                        Portland Class G                                                                       10%    1      --     --                                         4 (Inventive)                                                                         Portland Class H                                                                       10%    --     2.08   1.12                                       4a (Prior Art)                                                                        Portland Class H                                                                       17%    --     2.08   1.12                                       __________________________________________________________________________                            Fly Ash  Treated.sup.5                                  Density,                                                                              Water,  Defoamer.sup.4,                                                                        Microspheres,                                                                           Fibers,                                        Sample % By Weight                                                                            gal per 94 lb                                                                          % By Weight                                                                             % By Weight                                                                           lb per                                  No.    of Cement                                                                              Sack of Cement                                                                         of Cement                                                                               of Mix gal                                     __________________________________________________________________________     1 (Inventive)                                                                         55.8    --      --       --     9                                       1a (Prior Art)                                                                        116.5   --      100      --     9                                       2 (Inventive)                                                                         55.8    --      --       --     9                                       2a (Prior Art)                                                                        140.0   --      100      --     9                                       3 (Inventive)                                                                         44.3    0.05    --       --     9                                       3a (Prior Art)                                                                        109.8   --      100      --     9                                       4 (Inventive)                                                                         38.1    --      --       --     9                                       4a (Prior Art)                                                                        32.sup.6                                                                               --      --       0.3    9                                       __________________________________________________________________________      .sup.1 Condensation polymer product of ketone, aldehyde and sodium sulfit      ("CFR3 ™" from Halliburton Energy Services of Duncan, Oklahoma).            .sup.2 Sodium salt of alphaolefinic sulfonic acid.                             .sup.3 Cocoylamidopropylbetaine                                                .sup.4 Polydimethylsiloxane                                                    .sup.5 Chopped fibers were boiled with 10% NaOH at 80° C. for 1         hour; then cooled and washed until free from NaOH.                             .sup.6 % by weight of composition                                        

                                      TABLE IVB                                    __________________________________________________________________________     Comparative Test Results                                                                         Yield Strength                                                      Unconfined at 1000 psi                                                         Compressive                                                                          Tensile                                                                             Confining                                                                             Young's                                               Sample Strength,                                                                            Strength,                                                                           Pressure,                                                                             Modulus,                                                                               Poisson's                                     No.    psi   psi  psi    psi × 10.sup.-6                                                                  Ratio                                         __________________________________________________________________________     1 (Inventive)                                                                         280   136  1325   0.013 ± 0.0035                                                                      0.102835 ± 0.018011                        1a (Prior Art)                                                                        1092  133  1800   0.139 ± 0.0029                                                                      0.019314 ± 0.005359                        2 (Inventive)                                                                         280   136  1325   0.013 ± 0.0029                                                                      0.019314 ± 0.018011                        2a (Prior Art)                                                                        1260  175  2300   0.130 ± 0.0026                                                                      0.081631 ± 0.009028                        3 (Inventive)                                                                         282   109  1300   0.019 ± 0.0032                                                                      0.225041 ± 0.024208                        3a (Prior Art)                                                                        347   140  1500    0.077 ± 0.00085                                                                    0.106248 ± 0.025618                        4 (Inventive)                                                                         219    97  1275   0.026 ± 0.0021                                                                      0.084400 ± 0.006213                        4a (Prior Art)                                                                        350   125  2400   0.028 ± 0.0001                                                                      0.141158 ± 0.000791                        __________________________________________________________________________

From the results set forth in Table IVB and particularly the Young's moduli, it can be seen that the foamed compositions of this invention comprised of hydraulic cement, fumed silica, water, air, a foaming agent and a foam stabilizer have unexpected and surprisingly improved ductility and resiliency properties as compared to the prior art compositions tested.

EXAMPLE 5

Test samples of additional foamed cement compositions of this invention comprised of API Portland Class G hydraulic cement, an aqueous rubber latex, a latex stabilizer, a fluid loss control agent, a set accelerator, a defoaming agent, air, a foaming agent, and a foam stabilizer were prepared. For each test sample, a base unfoamed cement slurry including the defoaming agent was first prepared followed by foaming of the base slurry with a foaming agent and foam stabilizer as described in Example 2 above.

The various strength tests and modulus and ratio determinations described in Example 2 were conducted and determined.

The descriptions of the test samples are set forth in Table VA below and the results of the tests and determinations are set forth in Table VB below.

                                      TABLE VA                                     __________________________________________________________________________     Foamed Cement Compositions                                                     __________________________________________________________________________     Cement Composition Components                                                                    Aqueous    Fluid                                                               Rubber                                                                              Latex Loss                                                          Sand  Latex.sup.1                                                                         Stabilizer.sup.2,                                                                    Control                                                       (100 mesh),                                                                          gal per                                                                             gal per                                                                              Agent.sup.3,                                                                         Biopolymer.sup.4,                                       % by  94 lb                                                                               94 lb % by  % by                                        Sample                                                                             Hydraulic                                                                              Weight of                                                                            Sack of                                                                             Sack of                                                                              Weight of                                                                            Weight of                                   No. Cement  Cement                                                                               Cement                                                                              Cement                                                                               Cement                                                                               Cement                                      __________________________________________________________________________     1   Portland Class G                                                                       100   1    0.3   0.2   0.14                                        2   Portland Class G                                                                       100   i    0.3   0.2   0.14                                        3   Portland Class G                                                                       100   2    0.3   0.2   0.22                                        4   Portland Class G                                                                       100   2    0.3   0.2   0.22                                        5   Portland Class G                                                                       --    5    0.3   0.5   --                                          __________________________________________________________________________     Cement Composition Components                                                             Defoaming                                                                      Agent.sup.6,                                                                         Foaming                                                                              Foam  Water,                                                Accelerator.sup.5,                                                                    gal per                                                                              Agent.sup.7,                                                                         Stabilizer.sup.8,                                                                    gal per                                                                            Density                                           % by   94 lb % by  % by  94 lb                                                                              of Base                                                                            Foamed                                    Sample                                                                             Weight of                                                                             Sack of                                                                              Weight of                                                                            Weight of                                                                            Sack of                                                                            Slurry,                                                                            Density                                   No. Cement Cement                                                                               Water Water Cement                                                                             lb/gal                                                                             lb/gal                                    __________________________________________________________________________     1   4      0.02  4.3   2.2   6.28                                                                               16.3                                                                               14                                        2   4      0.02  4.3   2.2   6.28                                                                               16.3                                                                               12                                        3   4      0.02  5.1   2.6   5.28                                                                               16.3                                                                               14                                        4   4      0.02  5.1   2.6   5.28                                                                               16.3                                                                               12                                        5   2      0.02  5.2   2.6   3.33                                                                               17.5                                                                               15                                        __________________________________________________________________________      .sup.1 Aqueous styrene/butadiene (25%:75% by wt.) latex containing 50% by      weight Water ("LATEX 2000 ™" from Halliburton Energy Services).             .sup.2 Sodium salt of a sulfonated and ethoxylated compound having the         formula H(CH.sub.2).sub.12-15 (CH.sub.2 CH.sub.2 O).sub.15 SO.sub.3 Na         ("AVANEL S150 ™" from PPG Mazer).                                           .sup.3 Copolymer of "AMPS®" and N,Ndimethylacrylamide (U.S. Pat. No.       4,555,269).                                                                    .sup.4 Welan gum.                                                              .sup.5 Calcium chloride.                                                       .sup.6 Polydimethylsiloxane.                                                   .sup.7 Sodium salt of alphaolefinic sulfonic acid.                             .sup.8 Cocoylamidopropylbetaine.                                         

                                      TABLE VB                                     __________________________________________________________________________     Bond Strength And Resiliency Test Results                                      __________________________________________________________________________                                      Confined Triaxial                                                              Young's                                            Shear Hydraulic                                                                             Unconfined Uniaxial                                                                           Modulus                                            Bond  Bond   Young's    Compressive                                                                          (EX 10.sup.6)                               Sample                                                                              Strength,                                                                            Strength,                                                                             Modulus                                                                             Poissons                                                                             Strength,                                                                            Confining Pressure, psi                     No.  psi   psi    (EX 10.sup.6)                                                                       Ratio psi   500 1000                                                                               2000                                __________________________________________________________________________     1    303   780    --   --    --    --  0.039                                                                              --                                  2    244 (12.1).sup.1                                                                     660    --   --    --    --  0.029                                                                              --                                  3    322 (14.l).sup.1                                                                     775    --   --    --    --  0.048                                                                              --                                  4    287 (12.2).sup.1                                                                     660    --   --    --    --   0.0353                                                                            --                                  5     86 (15.4).sup.1                                                                     700    0.0025                                                                              0.102 392.sup.2                                                                            0.013                                                                              0.013                                                                              0.025                               __________________________________________________________________________     Confined Triaxial                                                                             Plastic    Bulk   Shear     Failure                                 Poisson's  Failure,   Compressibility                                                                       Modulus                                                                             Tensile                                                                             Envelope                                Ratio      psi        at 1000                                                                               at 1000                                                                             Strength                                                                            Friction                            Sample                                                                             Confining Pressure, psi                                                                   Confining Pressure, psi                                                                   psi, 10.sup.5                                                                         psi, 10.sup.4                                                                       (Briquet),                                                                          Angle,                              No. 500 1000                                                                               2000                                                                              500                                                                               1000                                                                               2000                                                                               psi    psi  psi  Degrees                             __________________________________________________________________________     1   --  0.1187                                                                             -- -- 3220                                                                               --  5.86   1.745                                                                               --   --                                  2   --  0.0436                                                                             -- -- 2000                                                                               --  9.44   1.389                                                                               --   --                                  3   --  0.1478                                                                             -- -- 3700                                                                               --  4.4    2.09 --   --                                  4   --  0.1808                                                                             -- -- 2200                                                                               --  5.47   1.482                                                                               --   --                                  5   0.078                                                                              0.128                                                                              0.171                                                                             1948                                                                              3096                                                                               4857                                                                               17.169 0.576                                                                               232.sup.3                                                                           9                                   __________________________________________________________________________      .sup.1 The number in parentheses is the test sample density in lb/gal.         .sup.2 The base pressure was 2220 psi.                                         .sup.3 The base pressure was 286 psi.                                    

From the results set forth in Table VB, it can be seen that the additional foamed cement compositions of this invention also have excellent bond strengths and resiliencies.

Thus, the present invention is well adapted to carry out the objects and advantages mentioned as well as those which are inherent therein. While numerous changes may be made by those skilled in the art, such changes are encompassed within the spirit of this invention as defined by the appended claims. 

What is claimed is:
 1. A well cement composition having improved mechanical properties including elasticity and ductility comprising:a hydraulic cement; fumed silica present in an amount in the range of from about 5% to about 30% by weight of hydraulic cement in said composition; sufficient water to form a pumpable slurry; a gas present in an amount sufficient to foam said cement composition; an effective amount of a foaming agent; and an effective amount of a foam stabilizer.
 2. The composition of claim 1 wherein said hydraulic cement is Portland cement.
 3. The composition of claim 1 wherein said water is present in an amount in the range of from about 22% to about 95% by weight of hydraulic cement in said composition.
 4. The composition of claim 1 wherein said gas is selected from the group of air and nitrogen and is present in said composition in an amount to produce a cement composition density in the range of from about 8 to about 16 pounds per gallon.
 5. The composition of claim 1 wherein said foaming agent is comprised of the sodium salt of alpha-olefinic sulfonic acid and is present in an amount in the range of from about 4% to about 9.5% by weight of water in said composition.
 6. The composition of claim 1 wherein said foam stabilizer is comprised of an amidopropylbetaine of the formula:

    R--CONHCH.sub.2 CH.sub.2 CH.sub.2 N.sup.+ (CH.sub.3).sub.2 CH.sub.2 CO.sub.2 .sup.-

wherein R is a C₁₀ -C₁₈ saturated aliphatic hydrocarbon group, an oleyl group or a linoleyl group, and is present therein in an amount in the range of from about 2% to about 5% by weight of water in said composition.
 7. A well cement composition having improved mechanical properties including elasticity and ductility comprising:Portland cement; fumed silica present in an amount in the range of from about 5% to about 30% by weight of said cement in said composition; water present in an amount in the range of from about 22% to about 95% by weight of said cement in said composition; a gas selected from the group of air and nitrogen present in an amount sufficient to foam said cement composition and produce a cement composition density in the range of from about 8 to about 16 pounds per gallon; a foaming agent comprised of the sodium salt of alpha-olefinic sulfonic acid present in an amount in the range of from about 4% to about 9.5% by weight of said water in said composition; and a foam stabilizer comprised of cocoylamidopropylbetaine present in an amount in the range of from about 2% to about 5% by weight of said water in said composition.
 8. The composition of claim 7 which further comprises an effective amount of a dispersing agent comprised of the condensation polymer product of a ketone, an aldehyde and sodium sulfite.
 9. A method of cementing in a subterranean well whereby the set cement can withstand impacts, shocks and cemented pipe movements subsequently generated by drilling and other well operations without cracking, shattering or otherwise failing comprising the steps of:introducing a cement composition which sets into a high strength solid mass having elasticity and ductility into said well, said cement composition comprising:a hydraulic cement, fumed silica present in an amount in the range of from about 5% to about 30% by weight of hydraulic cement in said composition, sufficient water to form a pumpable slurry, a gas present in an amount sufficient to foam said cement composition, an effective amount of a foaming agent, and an effective amount of a foam stabilizer; and allowing said cement composition to set in said well.
 10. The method of claim 9 wherein said hydraulic cement in said cement composition is Portland cement.
 11. The method of claim 10 wherein said water in said composition is present therein in an amount in the range of from about 22% to about 95% by weight of said cement in said composition.
 12. The method of claim 11 wherein said gas in said composition is selected from the group of air and nitrogen and is present therein in an amount to produce a cement composition density in the range of from about 8 to about 16 pounds per gallon.
 13. The method of claim 12 wherein said foaming agent in said composition is comprised of the sodium salt of alpha-olefinic sulfonic acid and is present therein in an amount in the range of from about 1.5% to about 10% by weight of water in said composition.
 14. The method of claim 13 wherein said foam stabilizer in said composition is comprised of an amidopropylbetaine of the formula:

    R--CONHCH.sub.2 CH.sub.2 CH.sub.2 N.sup.+ (CH.sub.3).sub.2 CH.sub.2 CO.sub.2 .sup.-

wherein R is a C₁₀ -C₁₈ saturated aliphatic hydrocarbon group, an oleyl group or a linoleyl group, and is present therein in an amount in the range of from about 0.75% to about 5% by weight of water in said composition.
 15. The method of claim 9 wherein said hydraulic cement in said composition is an API Portland cement.
 16. The method of claim 15 wherein said fumed silica in said composition is present therein in an amount of about 10% by weight of said cement in said composition.
 17. The method of claim 16 wherein said gas in said composition is nitrogen and is present therein in an amount sufficient to foam said composition and produce a cement composition density of about 13 pounds per gallon.
 18. The method of claim 17 wherein said foaming agent in said composition is the sodium salt of alpha-olefinic sulfonic acid and is present therein in an amount in the range of from about 4% to about 9.5% by weight of said water in said composition.
 19. The method of claim 18 wherein said foam stabilizer in said composition is cocoylamidopropylbetaine and is present therein in an amount in the range of from about 2% to about 5% by weight of said water in said composition.
 20. The method of claim 19 wherein said composition further comprises an effective amount of a dispersing agent comprised of the condensation polymer product of a ketone, an aldehyde and sodium sulfite. 